The middle point grounding method is a conventionally know grounding method for grounding a system power supply, which is used not only in AC power sources but also in high voltage DC power sources.
Also known in connection with the middle point grounding method is an electric leakage detecting device in which voltage is divided by resistor. As examples of such known art, the prior art discloses using two voltage division resistors connected between a positive power line and a negative power line of a DC power source and grounding the middle point of the two resistors. The prior art discloses teaches detecting electric leakage by dividing each voltage division resistor on a positive and a negative side into two sub voltage division resistors and comparing potentials at the middle points of the sub voltage division resistors and a reference potential. The prior art discloses detecting electric leakage by monitoring end-to-end voltage of voltages of two division resistors and detecting change in voltage ratio or voltage difference of the two voltage division resistors.
A middle point grounding system with voltage division resistors is also advantageous in that, in the event of an electrical shock accident on its power lines, the electric current that flows in the subject is lowered as the voltage division resistors are positioned to be juxtaposed to the subject.